Had to deal with this after innocently converting to Jagex account for that golden cape event.
I managed to get it working with TormStorm launcher install script (after several attempts, timeout galore) plus Drauxling post to avoid running rs3 (in my case) through wine. I'd assume osrs would also work (as I assume it's still java client). It was a "fun" way to lose an hour of playtime fiddling with Wine.
Personally I'd hope that they'd atleast endorsed running the launcher through Proton as to not complete kick less patient/techy Linux users out. Or, doom saying: is this a test to see the backlash/drop-out rate to decide to drop validated Linux support altogether?